Killer walrus theory undone

By John Gibb

Created 24/01/13

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University of Otago PhD student Robert Boessenecker holds a modern New Zealand fur seal skull and an artist's impression he has created, showing an ancient, and now extinct, walrus species. Photo by Peter McIntosh.

Robert Boessenecker may have just helped dispose of a myth
involving a prehistoric killer.

He believes that a mysterious and now extinct sea creature
which was once swimming off the coast of what is now modern
California more than 15 million years ago may not have been a
''killer walrus'' after all, despite earlier claims.

Mr Boessenecker, who hails from California and these days is
a University of Otago geology PhD student, has examined a
''new'' fossil found in Southern California and thrown doubt
on earlier claims that a ''killer walrus'' once existed.

Mr Boessenecker and co-author Morgan Churchill, of the
University of Wyoming, in the United States, undertook the
research, which was published in the online scientific
journal PLOS One. The new fossil-find, of the extinct walrus
Pelagiarctos, prompted a hypothesis different from an earlier
one that a ''killer walrus'' existed, preying on other
sizeable marine mammals and/or birds.

The large, robust size of the initially-found jaw bone, and
the sharp pointed cusps of the teeth - similar to modern
bone-cracking carnivores such as hyenas - initially suggested
that Pelagiarctos fed upon other marine mammals. But the new
fossil, a lower jaw with teeth, and more complete than the
original fossil, suggested to Mr Boessenecker and his
colleague that the Pelagiarctos was more of a fish eater,
lacking adaptations for being a ''killer walrus''.

The new find indicated this ''enigmatic walrus'' would have
appeared similar in life to modern sea lions, ''with a deep
snout and large canines'', and of similar size to some modern
male sea lions (about 350kg). Mr Boessenecker noted that
modern pinnipeds - seals, sea lions and walruses - whether of
small and large body sizes, were ''dietary generalists'',
tending to have diets rich in fish.

The study was supported by a University of Otago Doctoral
Scholarship, and grants from the Geological Society of
America, The Palaeontological Society, and a National Science
Foundation EAPSI Fellowship.